<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>重复请求问题</title>
</head>

<body>
    <button>点击发送</button>
    <script>
        // 获取元素
        var btn = document.querySelector('button');
        // 标识变量
        let isSending = false;// 是否正在发送Ajax请求
        let xhr = null;
        btn.onclick = function () {
            if (isSending) { xhr.abort(); } // 如果正在发送，则取消该请求，发送一个新的
            xhr = new XMLHttpRequest();
            // 修改 标识变量的值
            isSending = true;
            xhr.open('GET', 'http://127.0.0.1:8000/delay');
            xhr.send();
            xhr.onreadystatechange = function () {
                if (xhr.readyState === 4) {
                    // 修改标识符变量
                    isSending = false;
                }
            }
        }
    </script>
</body>

</html>